This invention relates to a wrap spring coupling of the type in which a coiled helical spring is telescoped over relatively rotatable input and output members. The invention more particularly relates to a wrap spring clutch of the type in which an annular control element or collar is shiftable axially relative to the input and output members. One end of the helical spring is connected to the control element while the other end of the spring is connected to one of the rotatable members so that the latter member, the spring and the control element all rotate in unison.
To engage the clutch, the control element is shifted axially into frictional engagement with the other rotatable member against the tensile force of the spring. Such engagement causes one end of the spring to rotate relative to the other so as to wrap the spring down on the members and cause the members to rotate in unison. When the clutch is disengaged, the tension in the spring pulls the control element out of frictional engagement with the rotatable member so that the spring may unwind and release the members for relative rotation.